Pressure-sensitive adhesive (PSA) constructions such as labels, tapes, decals and the like are known in the art. For example, PSA label constructions are commonly used to apply a particular facestock having a specific nature of printing to an object or article, and are especially useful where objects having low surface energies are to be labeled. PSA label constructions typically comprise a liner, a PSA layer disposed onto the liner, and a facestock laminated onto the PSA layer. The facestock is typically made from a web or sheet of paper, cardboard or plastic and is applied or laminated to the PSA layer sequentially at some time after the application of the PSA layer. The facestock is printed on with information or other indicia before or after it is laminated onto the PSA layer. Such conventional PSA label construction is applied to an object surface or other substrate surface by removing the liner to expose the PSA layer and placing the PSA layer into contact with the desired surface.
In the manufacture and production of PSA constructions, a substantial amount of the overall cost involved is attributed to the material costs for the different material layers, e.g., the PSA and the facestock, be it paper, cardboard, or plastic. The layer thickness and layer materials for such conventional PSA constructions have been selected to provide desired properties of convertibility, e.g., by conventional converting techniques such as by die-cutting and matrix-stripping, dispensibility, e.g, by conventional dispensing equipment such as by peel plate, and conformability, e.g., enabling the applied label to adhere to an irregular or deformable substrate surface without becoming detached or damaged.
It is known that the stiffness of a PSA construction will have an impact on its convertibility and dispensibility. As a rule of thumb, as the construction stiffness is increased so is convertibility and dispensibility of the construction. However, the conformability of a PSA construction is known to decrease as the construction stiffness is increased. Thus, the objective stiffness for a PSA construction is a compromise between convertibility/dispensibility and conformability. This compromise does not present a problem when designing a PSA construction for an application that does not require a high degree of conformity, such as a permanently flat surface. In such applications, the layer thickness and material choice is simply tailored to meet the desired convertibility/dispensibility and application criteria. This compromise does, however, present a problem when the construction application calls for conformability.
Prior art conformable PSA constructions having a Gurley stiffness of at least 10 mg, and more commonly of at least 20 mg or greater are known and are described in U.S. Pat. Nos. 5,186,782; 5,516,393; 4,713,273; and 5,451,283. Those patents exploited the idea that a proper differential between machine direction stiffness and cross dimension stiffness, with the latter being the lower of the two, could enable a heat-set film to be dispensed at high speeds, yet be suitable for flexible-film applications. Such label film might exhibit acceptable overall conformability to flexible substrates even though the film has less inherent conformability than polyvinyl chloride (PVC). The present invention provides a further breakthrough in the balance between dispensability and conformability, and achieves relatively low stiffness, yet conventionally dispensable labels which are well suited to applications calling for a high degree of conformability.
Specific applications calling for highly-conformable PSA constructions include those where the label is to be adhered to a small-diameter contoured surface or irregular surface. In such an application, unnecessary construction stiffness or rigidity could interfere with label's ability to conform and remain adhered to the underlying substrate surface. Additionally, these conventional PSA constructions are not manufactured in a most economically efficient manner.
Additionally, conventional PSA label constructions are not well suited for specific uses such as label applications where the label and underlying substrate are subjected to particular process conditions. For example, conventional PSA label constructions comprising a paper facestock and/or lacking necessary properties of conformability are known to be adversely affected when used on glass beverage bottles, during the washing/rinsing, filling and pasteurization process, due not only the decomposition of the paper facestock itself but to the failure of the PSA to remain adhered to the substrate surface. It is believed that such label lifting can be attributed to the rigidity or stiffness of such conventional PSA labels that, once the PSA is heated, causes the label and PSA to peel away and lift from the substrate surface. In such bottle label application, to avoid damage to the paper label, the paper labels are applied to a bottle after it has been rinsed, filled, and pasteurized, i.e., the label is "post applied". Generally, printed paper labels are post applied to filled bottles using aqueous adhesives or hot melt adhesives.
If post-applied paper labels are not completely adhered to the bottle, are misaligned on the bottle, or are otherwise incorrectly applied to the filled bottle, then the entire bottle and contents will be unusable and must be discarded. Thus, it is desired that glass bottles be labeled and inspected prior to being filled and pasteurized to eliminate defective bottles or labels.
It is known in the art to use certain high-performance acrylic PSAs to pre-apply plastic labels to glass bottles following bottle formation at a bottle manufacturing plant. Examples include Optiflex labels available from Flexcon, and Primeline label films available from Polykote Corporation. While these labels can generally withstand the bottle washing/rinsing, filling, and pasteurization operations at a bottle filling plant, they make use of specialized adhesives, such as solvent or emulsion acrylics, that are economically undesirable from a manufacturing perspective, making them an unattractive option when compared to conventional gum-type labels.
It is, therefore, desired to provide a PSA construction for use as a label, tag, tape, decal and the like in a manner that avoids the need to use a conventional facestock formed from paper, cardboard or plastic. It is desired that the printed message or indicia of such construction be protected from damage that can be caused by contact with adjacent physical objects or by exposure to moisture, weather and the like. It is desired that the PSA label construction be convertible by die-cutting and matrix-stripping methods at high speeds, be dispensable by conventional peel plate equipment, and be highly conformable. It is further desired that such PSA construction be capable of withstanding rinsing, filling, and pasteurization operations when applied to a glass beverage bottle to permit its use as a pre-applied label. It is also desired that the PSA label construction be manufactured in an economically efficient manner when compared to conventional PSA constructions